1. Field of the Invention
This ivnention relates generally to pressure vessels, and more particularly to a pressure vessel for use in fluid sample testing which has an improved vent cap closure.
2. Brief Description of the Prior Art
Pressurized containers are used in the testing of fluid samples, such as mud samples, wherein the substance are tested under simulated environment and/or static or circulating conditions to determine the effects of temperature and various chemical additives to determine the rheological, filtration, and chemical properties of the sample.
Some materials, such as drilling muds tend to thicken and in some cases to solidify when left under static conditions in a deep hot well bore. The thick or solidified mud impairs and sometimes prevents perforating, logging, or other drilling and completion operations. It is therefore highly advantageous to be able to predict the performance of the drilling mud under static, high temperature conditions and to prevent boiling and vaporization of the mud before it reaches the desired test temperature.
Commonly, the containers or vessels are cylindrical cup-shaped members having a screw on lid. The vessels are sealed and placed in an oven in an upright position, or horizontally on rollers and rotated while subjected to high temperatures within the oven. Often the vessels are connected through the lid to regulated pressure devices to pressurize the contents and to thermocouples or other sensing devices for motoring the conditions inside the container. At high temperatures and pressures, the threaded closure connection and the threaded connection for the regulating or sensing devices presents a hazardous connection. Occasionally a cap or threaded fitting will be blown off when then internal pressure is excessive.
A seal member on the threaded connections prevents leakage of pressure and/or hot liquids or gases from escaping through the threads. Often, pressure relief devices are placed on the container or closure member to protect against excessive pressure. The pressure relief devices may open or rupture when the oven is open which may jeopardize workers handling the container or in the immediate vicinity.
There are several patents which disclose various vent cap configurations, most of which are directed to caps designed for use on volatile fuel tanks.
Dolezal, U.S. Pat. No. 1,380,045 discloses a closure for fuel tanks with an internally threaded collar extending from the tank receiving a threaded cap having a central vent opening allowing air to enter as fuel is exhausted from the tank. An apertured disk is secured at the bottom of the cap and has another non-apertured disk spaced vertically thereabove. Fuel forced through the openings impinges on the upper disk and runs through the apertured disk back into the tank.
Martin, U.S. Pat. No. 1,509,969 discloses a closure for fuel tanks comprising a radial flange on a tube extending from the tank and a cap having internal lugs adapted to engage underneath the flange and leaf springs on the inner face of the cap opposite the lugs to press the flange against the lugs. The cap has a central air hole and a leather disk installed between the flange and the cap has a pair of laterally spaced holes to provide a tortuous path for air to enter and to aid in preventing liquid from splashing out when the vehicle is moving.
Griffin, Jr. et al., U.S. Pat. No. 2,298,938 discloses a vent closure for containers comprising an externally threaded casing extending from the tank and a domed cap having a central vent opening received thereon. A resilient, radially flanged tapered holder having a cavity at its upper end and a central hole extending from the cavity through the bottom end is captured between the cap with an apertured disk above the flanged end to form a seal. A plug of gas permeable or porous material is installed in the cavity beneath the aperture in the disk. The closure permits passage of gases therefrom but is impervious to the liquid stored in the container.
Hartman, U.S. Pat. No. 3,138,173 discloses an automatic pressure and vacuum cap having a two way vent cap which will admit air to the container to relieve the vacuum as the contents are withdrawn and vent the container when the contents are subjected to heat or excessive internal pressure.
Lee, U.S. Pat. No. 3,696,958 discloses a container closure which vents gases and/or vapors while retaining liquids. A liquid retaining diaphragm of film is sandwiched tightly between a flexible venting disk and a support disk, all of which are held on the container by a cap. The venting disk has a slit which is blocked by th film. Gas to be vented travels radially outward past the edge of the film then back radially inward on the other side of the film to where the slit is.
Kramer, U.S. Pat. No. 3,888,347 discloses a canister for pressurizing tennis balls which has an internally threaded cap with a groove cutting through the threads. An annular seal disk between the cap and the topen top end of the canister has a layer of sealant material on its bottom surface. The inner disk and outer portion of the cap are free to rotate with respect to one another. As the cap is unscrewed, pressure from the canister escapes through the groove in the threads.
Tupper, U.S. Pat. No. 4,165,816 discloses a vent cap having a resilient seal at the top surface of the threaded connection, a spring biased relief valve supported in a plate, and a groove extending from a cavity above the relief valve to the side of the plate. The threads between the cap and the neck of the container provide a fluid leakage space so that the relief/check valve can provide pressure relief between the interior of the container and the ambient atmosphere via the groove and the leakage space around the threads.
This invention is distinguished over the prior art in general, and these patents in particular by a pressure vessel comprising a cylindrical container externally threaded at the open top end and an O-ring seal in the top surface of the container side wall. A cylindrical disk encloses the top end of the container and has a raised neck portion surrounded by a recessed cavity having a rupture disk therein. An internally threaded cap member has a hole through its top wall through which the raised neck extends and forms an annular passageway therebetween, and has an enlarged diameter on its side wall above the threaded portion to provide an annular passageway surrounding the disk circumference.
The cap is screwed on the container over the cylindrical disk with the disk neck portion extending through the hole in the cap, and when hand tightened thereon compresses the disk on the O-ring to seal the container interior and isolate the threaded cap connection. The raised neck has an internal threaded bore and a valve seating surface for connecting the container with pressurizing apparatus for pressurizing the interior. The cap and container threads allow hand make up and provide a loose fit. The assembled unit has passageways around the cylindrical disk, between the disk neck portion and the hole in the cap, and through the thread convolutions of the cap and container connection to vent pressure, fluids, or gases on failure of the O-ring or bursting of the rupture disk.